Device for controlling hydraulic steering clutch and brake

ABSTRACT

A device for controlling hydraulic steering clutches and brakes in a crawler vehicle such as a bulldozer has a simple structure so as to be manipulated by a monolever. The device comprises a single steering lever (5), four proportional pressure control valves (1), (2), (3), (4), left and right steering clutch pistons (7), (7a) and left and right brake cylinders (8), (8a). The four valves are composed of two sets of valves, one set of two valves for steering clutches, in which the timing of the rise of hydraulic pressure is earlier, and one set of two valves for brakes, in which the timing of the rise of hydraulic pressure is later than the former.

FIELD OF THE INVENTION

The present invention relates to a device for controlling hydraulicsteering clutches and brakes used for a crawler vehicle such as abulldozer.

BACKGROUND OF THE INVENTION

The structures of hydraulic steering clutches and brakes will beexplained with reference to FIG. 4. In an actual vehicle, left and rightclutches and brakes in pairs are mounted on an axle 9. However, onlythose on the left side are exemplified in this figure.

During normal advance, the steering clutch 10 is turned on while thebrake 11 is turned off so that a power from an input shaft 12 istransmitted to a left output shaft 13 by way of the axle 9 and the leftsteering clutch 10, and accordingly, a drive sprocket 14 is driven.

In the case of steering, when for example a left steering lever 15 ispulled back from its neutral position, the operation of a hydrauliccontrol valve 17 is started through the intermediary of a link 16, andaccordingly, oil from a pump 6 flows into a left clutch piston 7 at aposition intermediate of a stroke so that the left steering clutch 10 isturned off.

Thus, the power on the axle is transmitted only to a right output shaftwhile a left output shaft 13 falls into a free condition, thereby thebulldozer turns moderately to the left.

From this condition, when the left steering lever 15 is pulled further,oil flows also into a left brake cylinder 8 by way of the hydrauliccontrol valve 17 so that the left brake 11 is turned on through theintermediary of a link 18, and accordingly, the left output shaft 13 ismade to be stationary, thereby the bulldozer turns sharply to the left.

Incidentally, when a brake pedal 19 is depressed, the left and rightbrakes are turned on through the intermediary of a link 20, andaccordingly, braking is performed in a straight travel condition.

However, such a conventional control device inevitably uses a large sizehydraulic control valve which is therefore disposed in an extra space inthe vehicle body and which is coupled to the steering lever through alinkage. Accordingly, the structure is complicated, resulting in anincrease in manufacturing cost.

Further, in order to enhance the steering ability in a monolever systemwhich is manipulated by a single lever, it is necessary to arrange leftand right hydraulic control valves in the vicinity of the steeringlever. However, such an arrangement has been difficult for theconventional large size control valve.

The present invention is devised in order to solve the above-mentionedproblems inherent to the conventional arrangement, and accordingly, oneobject of the present invention is to provide a device for controllinghydraulic steering clutches and brakes, which is simple in its structureand which can be manipulated by a monolever.

DISCLOSURE OF THE INVENTION

A device for controlling hydraulic clutches and brakes, according to thepresent invention, is composed of a single steering lever, fourproportional pressure control valves manipulated by the steering lever,and left and right steering clutch pistons and left and right brakecylinders which are connected to the output ports of the proportionalpressure control valves by means of conduits.

These four proportional pressure control valves consist of two sets ofvalves: one set of two proportional pressure control valves for steeringclutches, in which the timing of the rise of hydraulic pressure isearlier, and one set of two proportional pressure control valves forbrakes, in which the timing of the rise of hydraulic pressure is laterthan the former.

At first, when the steering lever is tilted, the proportional pressurecontrol valves for steering clutches are operated so as to move thesteering clutch pistons to turn off the clutches, accordingly, amoderate turn is performed. When the steering lever is further tilted,the proportional pressure control valves for the brakes are operated toactuate the brake cylinders, and accordingly, braking is effected,thereby a sharp turn is performed. With this arrangement, the steeringwith the use of a monolever can be made while having functionssubstantially the same as those of the conventional control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view illustrating an essential part of a devicefor controlling steering clutches and brakes, according to the presentinvention;

FIG. 2 is a plan view illustrating an arrangement of pressure controlvalves;

FIG. 3 is a graph showing the relationship between the stroke and thehydraulic pressure of the proportional pressure control valve; and

FIG. 4 is an explanatory view illustrating a conventional device forcontrolling steering clutches and brakes.

BEST CONFIGURATION FOR CARRYING OUT THE INVENTION

Explanation will be made of an embodiment of a device for controllingsteering clutches and brakes, according to the present invention, withreference to the drawings.

FIG. 1 is an explanatory view illustrating an essential part of thedevice for controlling steering clutches and brakes, and FIG. 2 is aplan view illustrating an arrangement of proportional pressure controlvalves.

Four proportional pressure control valves 1, 2, 3, 4, arranged as shownin FIG. 2, are mechanically linked to a single steering lever 5, andtheir inlet ports are connected to a hydraulic pump 6 while their outletports are connected respectively to left and right clutch pistons 7, 7aand brake cylinders 8, 8a by means of conduits.

The four proportional pressure control valves 1, 2, 3, consist of twogroups: one group including two proportional pressure control valves 1,4 for steering clutches, and the other group including two proportionalpressure control valves 2, 3 for brakes. Further, these valves arearranged so as to exhibit such a hydraulic characteristic that thetiming of the rise of hydraulic pressure of the proportional pressurecontrol valves 1, 4 for steering clutches is earlier that of theproportional pressure control valves 2, 3 for brakes as shown in FIG. 3.

In such a hydraulic control device, when the steering lever 5 is tiltedto the left in the direction of the arrow L, the proportional pressurecontrol valve 1 for a steering clutch is at first operated so that oilflows into the left clutch piston 7, and accordingly, a left steeringclutch 10 is turned off, thereby a vehicle turns moderately to the left.When the steering lever 5 is tilted further to the left, theproportional pressure control valve 3 for a brake is operated so thatoil flows into the left brake cylinder 8, and accordingly a left brake11 is turned on, thereby the vehicle turns sharply to the left.

When the steering lever 5 is tilted to the right in the direction of thearrow R, the proportional pressure control valve 4 for a steering clutchis operated so that oil flows into the right clutch piston 7a, therebythe vehicle turns moderately to the right, similar to that mentionedabove. When the steering lever is tilted further to the right, theproportional control valve 2 for a brake is operated so that oil flowsinto the right brake cylinder 8a, thereby the vehicle turns sharply tothe right, similar to that mentioned above.

It is noted that the proportional pressure control valves, which are ingeneral use for controlling pilot pressures of main control valves, areused in this embodiment for directly controlling actuators such aspistons so as to reduce the manufacturing cost. Accordingly, if thehydraulic pressure lacks due to internal loss or the like in theproportional pressure control valves, the setting pressure of thehydraulic pump 6 is boosted up for compensation.

The control device as mentioned above, uses small size proportionalpressure control valves, and accordingly, it is possible to facilitatethe use of a monolever system, thereby the steering ability can beenhanced.

Further, different from a method of using proportional pressure controlvalves in general, actuators are driven directly by proportionalpressure control valves without using main control valves, andaccordingly, the necessity of intermediate links and the like can beeliminated, and thereby it is possible to reduce the cost.

INDUSTRIAL APPLICABILITY

The present invention is effectively used for a device for controllinghydraulic steering clutches and brakes used in a crawler vehicle such asa bulldozer, and in particular, the structure thereof is simple so thatit is effectively used as a control device which can be manipulated by amonolever.

What is claimed is:
 1. A device for controlling hydraulic left and rightsteering clutches and left and right brakes in a hydraulic steeringdevice mounted on an axle of a crawler vehicle and adapted tohydraulically turn on and turn off a steering clutch, characterized by asingle steering lever, four proportional pressure control valvesmechanically manipulated by said single steering lever, and left andright steering clutch pistons and left and right brake cylindersconnected respectively to outlet ports of said proportional pressurecontrol valves through the intermediary of conduits, wherein said fourproportional pressure control valves are composed of two sets, one setof two proportional pressure control valves for said left and rightsteering clutch pistons, in which the timing of the rise of hydraulicpressure is earlier, and one set of two proportional pressure controlvalves for said left and right brake cylinders, in which the timing ofthe rise of hydraulic pressure is later than that of the former, theproportional pressure control valve for said left steering clutch pistonand the proportional pressure control valve for said left brake cylinderbeing positioned with respect to the single steering lever so as to beactuated by tilting of the single steering lever to the left, and theproportional pressure control valve for said right steering clutchpiston and the proportional pressure control valve for said right brakecylinder being positioned with respect to the single steering lever soas to be actuated by tilting of the single steering lever to the right,with the four proportional pressure control valves being arranged withrespect to the single steering lever so that a degree of tilting of thesingle steering lever required for an operation of a pressure controlvalve to provide a rise of hydraulic pressure to a brake cylinder isgreater than a degree of tilting of the single steering lever requiredfor an operation of a pressure control valve to provide a rise ofhydraulic pressure to a steering clutch piston.
 2. A device inaccordance with claim 1 wherein each of said proportional pressurecontrol valves is connected directly by a respective conduit to arespective one of said left steering clutch piston, said right steeringclutch piston, said left brake cylinder, and said right brake cylinderso as to provide direct control thereof.
 3. A device for controllinghydraulic left and right steering clutches and left and right brakes ina hydraulic steering device mounted on an axle of a crawler vehicle,characterized by a single steering lever, four proportional pressurecontrol valves mechanically manipulated by said single steering lever,and left and right steering clutch pistons and left and right brakecylinders connected respectively to outlet ports of said proportionalpressure control valves through the intermediary of conduits, whereinsaid four proportional pressure control valves constitute a leftsteering valve, a left brake valve, a right steering valve, and a rightbrake valve, and wherein said single lever is associated with said fourproportional pressure control valves such that a degree of tilting ofthe single steering lever required for an operation of a pressurecontrol valve to provide a rise of hydraulic pressure to a brakecylinder is greater than a degree of tilting of the single steeringlever required for an operation of a pressure control valve to provide arise of hydraulic pressure to a steering clutch piston so that a tiltingof said lever in a left direction first operates the proportionalpressure control valve connected to said left steering clutch piston toeffect a moderate turn to the left and a further tilting of said singlelever in the left direction operates the proportional pressure controlvalve connected to said left brake cylinder to effect a sharper turn tothe left, while a tilting of said lever in a right direction firstoperates the proportional pressure control valve connected to said rightsteering clutch piston to effect a moderate turn to the right and afurther tilting of said single lever in the right direction operates theproportional pressure control valve connected to said right brakecylinder to effect a sharper turn to the right.
 4. A device inaccordance with claim 3 wherein each of said proportional pressurecontrol valves is connected directly by a respective conduit to arespective one of said left steering clutch piston, said right steeringclutch piston, said left brake cylinder, and said right brake cylinderso as to provide direct control thereof.
 5. Apparatus in accordance withclaim 4, wherein the proportional pressure control valves connected toone of said left steering clutch piston and said right steering clutchpiston form a first set of proportional pressure control valves andwherein the proportional pressure control valves connected to one ofsaid left brake cylinder and said right brake cylinder form a second setof proportional pressure control valves, wherein the timing of the riseof hydraulic pressure is earlier in said first set than in said secondset.